CA1149449A - High rate carbon cathode, method of making, and electrochemical cell including the cathode - Google Patents

High rate carbon cathode, method of making, and electrochemical cell including the cathode

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Publication number
CA1149449A
CA1149449A CA000365694A CA365694A CA1149449A CA 1149449 A CA1149449 A CA 1149449A CA 000365694 A CA000365694 A CA 000365694A CA 365694 A CA365694 A CA 365694A CA 1149449 A CA1149449 A CA 1149449A
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CA
Canada
Prior art keywords
cathode
mixture
polytetrafluoroethylene
carbon
high rate
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired
Application number
CA000365694A
Other languages
French (fr)
Inventor
Sol Gilman
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United States Department of the Army
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United States Department of the Army
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Filing date
Publication date
Application filed by United States Department of the Army filed Critical United States Department of the Army
Application granted granted Critical
Publication of CA1149449A publication Critical patent/CA1149449A/en
Expired legal-status Critical Current

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Classifications

    • HELECTRICITY
    • H01ELECTRIC ELEMENTS
    • H01MPROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00Electrodes
    • H01M4/86Inert electrodes with catalytic activity, e.g. for fuel cells
    • H01M4/96Carbon-based electrodes
    • YGENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02EREDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/30Hydrogen technology
    • Y02E60/50Fuel cells

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  • Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • General Chemical & Material Sciences (AREA)
  • Primary Cells (AREA)

Abstract

Abstract of the Disclosure A high rate carbon cathode is made by mixing a carbon powder having a surface area of about 1000 square meters/gram with polytetrafluoroethylene and a sufficient amount of water to form a coherent mixture. The mixture is applied to an electrically conductive screen; the cathode formed while wet to an intermediate thickness, the cathode vacuum dried at about 100 degrees C.
and the cathode cold compressed to obtain a final electrode porosity of greater than 80 percent. The cathode can be used in lithium primary cell using a solution of an inorganic lithium salt in sulfuryl chloride as the electrolyte.

Description

~1~9 ~9 This invention relates to a high rate carbon cathode, to a method of making the cathode, and to an electrochemical cell including the cathode.
A number of oxides and oxyhalides of sulfur, selenium and phosphorus can be utilized as liquid phase cathode reactants in primary lithium battery cells. Such oxides and oxyhalides include sulfur dioxide, phosphorous oxy-chloride, selenium oxychloride, thionyl chloride and sulfuryl chloride. These compounds can be dissolved in an inert or organic solvent, mixed with each other or used as the sole electrolyte solvent.
One of the most promising of these primary cell systems is the lithium-thionyl chloride cell. One of the most successful cell formulations uses a solution of lithium aluminum chloride in thionyl chloride as the elec-trolyte and a Teflon~-bonded carbon electrode as the cathode.
It has also been disclosed that the use of sulfuryl chloride as the electrolyte solvent affords the highest open circuit voltage of any known primary cell. The difficulty with the use of sulfuryl chloride is that its closed circuit voltage, capacity, and as a result its energy density is inferior to that of thionyl chloride which has been the most popular of the oxychloride solvents for primary cells.
The general object of this invention is to provide a high rate electrochemical cell. A more particular object of the invention is to provide such a cell that is characterized by low cathode polarization and increased cathode life and energy density. A particular object of the invention is to provide such a cell that effectively uses sulfuryl chloride as the electrolyte solvent.
It has now been found that the aforementioned obiects can be attained by making the cathode for the cell by the steps of:

,~
.

9~9 ~ A) mi~ing a carbon powder havin~ a surface area of about 1000 square meters per ~ram with polytetrafluoroetllylene and a sufficient amount of water to form a coherent mixture, ~ B) applying the mixture to an electrically conductive screen, (C) forming the cathode while wet to an intermediate thickness, (D) vacuum drying the cathode at a temperature of about 100 degrees C, and (E~ cold compressing the cathode to obtain a final electrode poros-ity of greater than 80 percent.
In Step (A), the carbon powder used will preferably have a surface area as determined through gas absorption of about 1000 to 1200 square meters per gram. Such carbon powders include furnace blacks and channel blacks of which a furnace black is preferred. The polytetrafluoroethylene is used in an amount of 7 to 14 percent by weight on a dry basis of the coherent mixture.
In Step (B), the mixture is applied to the electrically conductive screen by conventional techniques. The screen material is preferably resis-tant to corrosion in sulfuryl chloride. Such a material is pure nickel or a high nickel steel. Moreover, it is preferred that the screen ~e characterized by a maximum tortuosity for good anchoring of the polytetrafluoroethylene-carbon mixture and to provide high electronic conduction.
In Step (C), the cathode is compressed while still moist to anintermediate thickness greater than the final electrode thickness.
In Step (D), drying is preferably carried out under vacuum or in the presence of an inert gas to prevent oxidation of the screen. The dry cathode polytetrafluoroethylene-carbon mix is now highly cracked and poorly adherent to the screen.
In Step (E), the cathode i6 cold compressed to a value less than the final thickness in a suitable frame. The natural resiliency of the cathode causes it to re-expand to the final thickness when pressure is released. The cold-compression step is found to "heal" the cracks in the polytetrafluoro-ethylene-carbon mixture leaving micro-tunnels whicll contribute to the very high 11 L~9~49 porosity of greater than 80 percent of the final structure. That porosity is responsible for the high capacity of the electrode. The high surface area of the carbon is responsible for the high closed circuit voltages obtained.
Previously reported inferior results for sulfuryl chloride vis-a vis thionyl chloride, were due to the necessity for using low-area carbon black which does not require the processing described above. Cathodes using low area carbon, as for example, acetylene black having a gas adsorption area of 60 meter /gram are adequate for use with thionyl chloride, but serve poorly for sulfuryl chloride.

A cathode according to the invention is made in the following manner.
One gram of a furnace black carbon powder having a surface area of about 1000 square meters per gram is mixed with an emulsion containing 0.12 grams of polytetrafluoroethylene and a sufficient amount of water to yield a stiff paste. The paste is then applied to a 2.5 cm x 2 cm expanded nickel support screen. The support is prepared by welding 2 thicknesses of screen together, with the mesh out of registration so as to provide maximum tortuosity.
While still moist, the electrode is compressed to an intermediate thickness of 0.0615 inch. After vacuum drying for 24 hours at 99 degrees C, the cathode is compressed in a 0.025 inch frame and after re-expansion has a final thick-ness of 0.035 inch. The cathode has a porosity of 87 percent.
A complete cell can be conveniently assembled in an all-Teflon jig with the plane of the electrodes parallel to the bottom of the jig. The cathode as prepared above is placed between two lithium anodes. A lithium foil electrode placed in the same plane as the cathode serves as a reference.
A 0.012 inch thick glass "filter paper" provides mechanical separation between the cathode and the lithium counter-electrodes, f`acing it on each side. The lithium anodes are fabricated by pressing nickel Exmet*into a 0.050 inch thick lithium foil. After assembling the cell and adding 3cc of a 1.5 molar solution of lithium aluminum chloride in sulfuryl chloride as the electrolyte, a Teflon weight is applied to the cell the help maintain good contact between the cell components.

*denotes trademark.

Thc improvcment in closed circuit voltagc over a wide range of eurrent densitics is upwards of 0.3 volt when compared to the same cell using thionyl chlori(lc as the electrolyte solvent and Shawinigan black in the `^~ cathode as can bc scen by referring to the TABLE. Reference to the TABLE
also indicatc that further improvement in cell voltage is obtained when the clcctrolyte is pre-saturated with chlorine. The improvement in cell capacity for SO2C12 as compared with SOC12 is upwards of 10% for cells with or without C12 pre-saturation.

TABLE

Current Density mA/cm (based on Li/SOCl2 Li/SO2Cl2 Li/(SO2C12+C12) lx~, onc sidc) Ccll Voltagc Ccll ~oltagc Ccll Voltagc 0.1 3.67 3.91 3.93 0.2 3.59 3.89 3.91 0.5 3.56 3.87 3.89 1.0 3.51 3.86 3.87
2.0 3.50 3.83 3.84 5.0 3.45 3.79 10.0 3.31 3.67 20.0 3.14 3.31 In lieu of pre-saturation with chlorine, one may add other halogens andlor interhalogens to the electrolyte. For example, the invention contem-plates the addition o~ fluorine, iodine trichloride, combinations of chlorine and iodine trichloride, etc.
One may also modify the electrolyte by adding various inorganic solvents such as thionyl chloride and phosphorous oxychloride and such organic solvents as propylene carbonate, acetonitrile, etc. These solvents are added to modify the physiochemical properties of the electrolyte such as the conduc-tivity, boilin~ int, r--ee~;n~ p~int, va~ I)rcssurc, ctc.
~ ~ ~ s ~

ln lieu oC li~llium as the anodc, one may use othcr active metals such as magnesium, calcium, and alloys of lithium, magnesium and calcium with each other and with other mctals. Whcn one substitutes another active metal for lithium, onc may find it advantageous to use the corresponding cationic metallic ion in the electrolyte.
I wish it to be understood that I do not desire to be limited to the exact details as described for obvious modifications will occur to a person skilled in the art.

Claims (14)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. Method of making a high rate carbon cathode, said method including the steps of:
(A) mixing a carbon powder having a surface area of about 1000 square meters/gram with polytetrafluoroethylene and a sufficient amount of water to form a coherent mixture;
(B) applying the mixture to an electrically conductive screen;
(C) forming the cathode while wet to an intermediate thickness;
(D) vacuum drying the cathode at a temperature of about 100 degrees C; and (e) cold compressing the cathode to obtain a final electrode porosity of greater than 80 percent.
2. Method according to claim 1 wherein in Step (A) the polytetrafluoro-ethylene is about 7 to 14 weight percent on a dry basis of the coherent mixture.
3. Method according to claim 1 wherein the electrically conductive screen is resistant to corrosion in sulfuryl chloride.
4. Method according to claim 3 wherein the electrically conductive screen is a nickel screen having a high tortuosity for good anchoring of the polytetrafluoroethylene-carbon mixture.
5. Method of making a high rate carbon cathode, said method consisting of (A) mixing a carbon powder having a surface area of about 1000 square meters/gram with polytetrafluoroethylene and a sufficient amount of water to form a coherent mixture, the polytetrafluoroethylene being about 7 to 14 weight percent on a dry basis of the coherent mixture, (B) applying the mixture to a nickel screen having a high tortuosity for good anchoring of the polytetrafluoroethylene-carbon mixture, (C) forming the cathode while wet to an intermediate thickness, (D) vacuum drying the cathode at a temperature of about 100 degrees C, and (E) cold compressing the cathode to obtain a final electrode poros-ity of greater than 80 percent.
6. A high rate carbon cathode comprising an electrically conductive screen and a cold compressed coherent polytetrafluoroethylene-carbon powder mixture anchored to said screen, the polytetrafluoroethylene being about 7 to 14 weight percent of the coherent mixture, the carbon powder having a surface area of about 1000 square meters/gram, and the cathode having a poro-sity of greater than 80 percent.
7. A high rate carbon cathode according to claim 6 wherein the electrically conductive screen is resistant to corrosion in sulfuryl chloride.
8. A high rate carbon cathode according to claim 7 wherein the elec-trically conductive screen is a nickel screen having a high tortuosity for good anchoring of the polytetrafluoroethylene-carbon powder mixture.
9. An electrochemical cell using a solution of an inorganic lithium salt in sulfuryl chloride as the electrolyte, said electrochemical cell comprising a lithium anode and a high rate carbon cathode spaced from said lithium anode, wherein said high rate carbon cathode comprises an electrically conductive screen and a cold compressed coherent polytetrafluoroethylene-carbon powder mixture anchored to said screen, the polytetrafluoroethylene being about 7 to 14 weight percent of the coherent mixture, the carbon powder having a surface area of about 1000 square meters/gram, and the cathode having a porosity of greater than 80 percent.
10. An electrochemical cell according to claim 9 wherein the electrolyte is saturated with a member selected from the group consisting of chlorine, fluorine, iodine trichloride, and combinations of chlorine and iodine trichlor-ide.
11. An electrochemical cell according to claim 10 wherein the electrolyte is saturated with chlorine.
12. An electrochemical cell according to claim 10 wherein the electrolyte is saturated with fluorine.
13. An electrochemical cell according to claim 10 wherein electrolyte is saturated with iodine trichloride.
14. An electrochemical cell according to claim 10 wherein the electrolyte is saturated with combinations of chlorine and iodine trichloride.
CA000365694A 1980-04-14 1980-11-18 High rate carbon cathode, method of making, and electrochemical cell including the cathode Expired CA1149449A (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US140,369 1980-04-14
US06/140,369 US4303604A (en) 1980-04-14 1980-04-14 Method of making a high rate carbon cathode

Publications (1)

Publication Number Publication Date
CA1149449A true CA1149449A (en) 1983-07-05

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4790969A (en) * 1987-07-16 1988-12-13 Eveready Battery Company Dry molded cathode collector for liquid cathode systems

Family Cites Families (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3442715A (en) * 1965-03-01 1969-05-06 Monsanto Res Corp Method of making diffusion membrane electrodes from visco elastic dough
US3385736A (en) * 1965-03-01 1968-05-28 Monsanto Res Corp Method of making electrode from viscoelastic dough
US3389200A (en) * 1966-03-30 1968-06-18 Dow Chemical Co Process for producing compressed vermicular graphite structures
US3655585A (en) * 1969-08-28 1972-04-11 Mallory & Co Inc P R Method of preparing cathodic electrodes

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US4303604A (en) 1981-12-01

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